Directindicating ohmmeter with hand driven dc generator. From these above mentioned, it results that the measurement methods of electrical resistance have to be very varied. Publication date 1912 topics electric resistance publisher new york, mcgrawhill book company. The most commonly used method of measuring the earth resistance of an earth electrode is the 3point measuring technique shown in figure 1. Pdf electrical conductivity and resistivity michael b. Standard test method for electrical resistance of tires.
The electrical resistance er technique is an online method of monitoring the rate of corrosion and the extent of total metal loss for any metallic equipment or structure. Use of a capacity in connection with a wheatstone bridge for highresistance measurements. By a special construction, it is arranged so that contact can be made at any point along it, and it is therefore equivalent to a high resistance wire. The study of electrical resistance measurement methods using virtual instruments article pdf available june 2010 with 952 reads how we measure reads. The first page of the pdf of this article appears above. The study of electrical resistance measurement methods. We present a method and the corresponding instrumentation to measure the electric resistance of electrolytic solutions in conductivity cells. The measurement of earth resistance is made by the potential fall method. Introduction contact resistance measurement and his application domain are fairly extensive. Key words contact resistance, measurement, loop resistance 1. This method requires that the unknown resistance is connected into a special circuit with two separate meters. Electrical resistivity is a key physical property of all materials. Standard test methods for dc resistance or conductance of. The value of resistance in engineering varies from very small value like, resistance of a transformer winding, to very high values like, insulation resistance of that same transformer winding.
Ohmmeter ohmmeter method of measuring resistance ohmmeter circuit diagram series and shunt type this video explains basics of ohmmeter with all of its types. The suitability of a particular method for resistance measurement depends upon the relative values of resistance under measurement and the resistance of the meters. Methods of measurement of properties of electrical. Electrical resistance and the resistor introduction ohms law is the most fundamental equation in electric circuit analysis. Measuring earth resistance for electrical grounding systems the simplest and somewhat misleading idea of a good ground for an electrical system is a section of iron pipe driven into the earth with a wire conductor connected from the pipe to the electrical circuit fig.
Page 207 this ratio may take a value of two or more. In this post we will discuss about the ohmmeter in. Prospecting for good low resistance ground locations, or obtaining. Astm d5682 18 standard test methods for electrical. The study of measuring methods for electrical resistance.
Methods of measuring electrical resistance open library. Electric resistance, accessible book methods of measuring electrical resistance open library. This is why the reading of insulation resistance is normally taken after 15 seconds or 1 minute or sometimes after 10 minutes during the test. Method for measurement of resistance ammetervoltmeter. The change of resistance cor method for determining the.
The 3point method, called the fall of potential method. Wheatstonebridge method of measuring a resistance from 10 to megohms. This may, or may not, be a suitable low resistance path for electric. Major cardews electrometer method of measuring a high re sistance. We can determine an unknown resistance in figure 1 by applying ohms law to the readings obtained from the voltmeter and ammeter. Resistance measurement methods diy electronics projects. Resistance measurement methods electrical academia.
Methods of measuring electrical resistance by northrup, edwin f. Methods of measuring electrical resistance edwin fitch. To tell the truth i could not find a suitable book on the whole subject and therefore i. Sensor or transducer is an input device convert the quantity under measurement into a detectable signal form. However the resistance rel caused by polarisation of the electrodes and the field effect interferes with the measurement, and both rsol and rel are measured. Introduction to electrical resistance er monitoring. For every range, any measurement methods are specific, pursuing elimination of parasite resistance influence. This method is derived from the 4point method which is used for soil resistivity measurements.
Electrical field, e, is the negative of the gradient in electrical potential, i. The electrical resistivity of different materials at room temperature can vary by over 20 orders of. It has a moving contact c and a scale of divisions. The division point between the two methods is at the resistance for which the relative errors given by the two methods are equal. B test methods for measuring resistance of electrical 1 this guide is under the jurisdiction of astm committee b02 on nonferrous. Methods of measuring electrical resistance pdf download.
It has been found that the sorption units lose or gain moisture from the surrounding soil. Methods of reducing the effects of polarisation are explained on page 16. An earth electrode and earth electrode resistance are defined in bs 7671 as. Earth electrode conductive part, which may be embedded in the soil or in a specific conductive medium, e. K 110 measurement of the electrical resistance of tyres 3. The most common methods of measuring the resistance of an. Electrical resistivity is a basic material property that quantifies. Methods of measuring electrical resistance by northrup, edwin f 2 editions. Aknowledgeofearthresistivityorspecificresistancemay be of value in determiningsomething of the composition ofearth, such for example, as moisture content, whether it contains oil, ore. Its power lies in its ability to accurately measure the properties of a sample of any arbitrary shape, as long as the sample is approximately twodimensional i. Earth resistance is measured in two ways for two important fields of use.
Astm b, standard test methods for measuring resistance of electrical connections static. Output state provides an indication of the value of the measurement readout device or recording. Methods of measuring soil moisture in the field by a. Com 99 washington street melrose, ma 02176 phone 7816651400 toll free 18005178431 visit us at. Although methods of measuring insulation and ground resistance are given in this code, more complete discussions may be found in 5, 7, 11. Methods of measuring electrical resistance science. Leon markwell, senior engineer at the iet, discusses the inspection and testing of earth electrodes. Signal conditioning modifies the transducer signal into a desired form e. If you like methods of measuring electrical resistance pdf download, you may also like.
It states that the amount of electric current flowing in a circuit is directly proportional to the voltage applied to the circuit, and inversely proportional to its resistance. In the figure shown below e is the earth electrode under rest, and a is an auxiliary earth electrode positioned so that two. In this method we use a cylindrical cell and follow the simplest electrical model for an electrochemical cell, which is the electrolyte resistance in. I lecture on electrical measurements to students of electrical engineering, robotics and informatics. Johnson contributions to the hydrology of the united states geological survey watersupply paper 1619u evaluates methods for measuring soil moisture and describes the equipment used united states government printing office, washington.
The test fixture has a shielded sense cable and 2 standard banana plug cables for connection to the measuring instrument. Basic techniques for accurate resistance measurement. Broadly speaking, earth resistance is the resistance of soil to the. Although a multimeter works quite well if we need a rough value of resistance, but for accurate values. There are several instruments for measuring insulation resistance of an electrical equipment. This method is derived from the 4point method which is used for soil resistivity measurements the 3point method, called the fall of potential method, comprises the earth electrode to be measured and two other electrically independent test. If youre measuring resistance near to the source, youll get different readings than. Resistance is one of the most basic elements encountered in electrical and electronics engineering.
The resistance area of the earth electrode is the area of the soil around which a voltage gradient is measured with a commercial instrument. It is often necessary to accurately measure the resistivity of a given material. Measurement of earth resistance by potential fall method. You run 2 wires on either side of the resistor, then force the.
A guide to low resistance testing test equipment depot. Basic techniques for accurate resistance measurement 2. Direct deflection method with the use of high sensitivity galvanometer. Pdf a method for the measurement of the resistance of. Determining effectiveness of ground grids and connections that are used with electrical systems to protect personnel and equipment. This method can also been applied to calibration loop resistor standard. Soil moisture measurements by electrical resistance. Current, i, results from the flux of charged particles.